mccrudden



1,452,123v J. C. R. MCCRUDDEN MACHINE GUN 4 Sheets-Sheetv l .n .QN wm n Nm m. euhm wkn www@ Q m.

Apr. 17, 1923.

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J. c. R. MCCRUDDEN MACHINE GUN FiledvJune 19 1920 4 Sheets--Sheet 2 A@ Nw RS* R Patented Apr. 17, 19h23.

UNITED vSTAT-ris JOHN c. R. MCCRUDDEN, or HURSTVILLE, NEAR SYDNEY, NEw'soU-'rn WALES,

AUSTRALIA. 1

MACHINE GUN.

i Application led .Tune 19, 1920,'- Serial N'o. 390,153. i

To aZZ lwhom t may concern: Be it known tliail, JOHN CHARLES REGL- NALD lVIcCnUDDEN,subject of the King of.

Great Britain and Ireland, residing. at Fleurbaix, Haig Street, Hurstville, near Sydney, New South Vlales, Australia, vhave invented certain new and 'useful Improvements in Machine Guns, of which the following is a specification. Y This invention relates to machine guns of the automatic recoil type, having an axially moving breech block With key locking means. The machine gun inv which this invention consists is sutliciently low in weight to permit it to be used as a shoulder arm in emergencies and to be moved and handled by one man under all service conditions. The novel features and detail of structure hereinafter particularly described have been devised inter alia with a view to economising time and labour in recharging the gun with ammunition; to making the gun capable of sustained operation in long bursts of fire; to -providing etlicient and readily controlled means for regulating the rate of iire and varying that rate whilst the gunis in o eration; to carrying away heat from the c iamber and barrel at a rate which will enable the gun to be used with safety in prolonged bursts of fire; 3o to adequately protecting the gun parts against fouling or injury by sand, mud or dust, and facilitating cleaning of the parts; to providing a rugged design of parts without elements of delicate proportions which $5 would be liable to suffer injury in prolonged or rough use; to rendering of the weapon convertible without structural change of parts for use optionally as a single tire shoulder arm, or as an automatic repeater arm 0 fixed or laid in an appropriate support; to augmenting the capacity of the gun for use under exceptional conditions where long bursts of fire are called for, by providing readily detachable and replaceable maga- 5 zines of large capacity which contain a very large number of cartridges; to providing means for effectively smothering the eXplosion flash and muiiling the explosion report, thereby to make the gun more useful for o the reason that it will not disclose its position to an enemy readily, either in daylight or night service, its operators thus better eluding detection by opposing forces, to providing a design, which is structurally adapt- 5 ed for the fitting to it of water cooling means PATENT,OFFICE;y

f to replace its standard air cooling means for i restrainingthe temperature in the barrel" within a safe working limit; to permittingV ready removal'and replacement of all un- Iixed elements without rc'courseto workshop tools,. thus facilitating the 'dismantling of the gun andv its ready refassenibling, and lotherwise.generally to providing a military Vservice weapon'havingv all-roundutility for rough field and trench, workand for airplane and anti-airplane lighting and for naval purposes.

yIn the-accompanying drawings, Fig; 1 is a side elevational view of a gun accordingV to the presen-t invention complete, as it appears with the sighting leaf raised, and the magazine set in the throat in the breech, the magazine being of a new type adapted for carrying or more small arm service cartridges of .303 or like standard dimension.

F ig. 2 is asectional elevation of the cen.-

tral portion of the gun on an enlarged scale,

displaying the parts in cocked position ready for firing, with a cartridge in the barrel chamber, and the'bolt locked; F ig. 3 is a horizontal plan on the section line3-3Fig.2; v

Fig. 4 is a longitudinal sectional elevation showing the gun parts in the position theyk occupy during the recoil, the barrel and the breech carriage being fully recoiled, and the 'bolt unlocked and commencing itsrecoil movement in the carriage; y

Fig. 5 is a similar sectional elevation showing the position of the gun parts When the bolt is fully recoiled, the barrel and breech carriage restored to; normal position in the body casing, and the bolt about to begin its closing movement in which it is brought up to the barrel chamber, and in moving forward takes with it a fresh cartridge from the top 'of the magazine; in this figure the 'recoiling parts are shown in full lines, whilst the steady parts ofthe gun are indicated in dotted lines;

Fig. 6 is a perspective'view of the breech carriage shown attached to the barrel breech; i

Fig. 7 is a perspective view of the bolt latch; v

Fig. 8 is a perspective View of the bolt;

Fig. 8a is a perspective view of the trace head on the bolt restoring spring:

ing the lock assembly with the gun parts in the same position as in Fig. 2, thatis, ready for firing; the trigger safety catch is shown set;

Fig. 10 is a similar View showing only the Fig. 11 is a fragmentary .View showing some of the lock parts as the same appear when the tiring pin has been reset during the recoil movement; the trigger'in this case', as well as 1n Fig. 10 being shown ulled;

Fig. 12 is a transverse sectiont `View on @midway of their length to give clearance Afor the latch, and having bearing eyes 34 1n the plane 12-12 Fig. 9;

Fig. 13 is a transverse sectional vien7 on the plane 12-13 Fig. 9;

Fig. 14 is a fragmentary perspective View of the hand grip and the trigger assembly;

Fig. 15 is a perspective view of the breech body casing. the rear end of which is fixed to the butt head;

Fig. 1G is a fragmentary side elevational view explanatory of the casing latch by which the body casing is fixed to the buttv head;

Fig. 17 is a fragmentary rearelevational view corresponding with Fig. 16; Y

Fig. 18 is a longitudinal sectional View through the forward end of the barrel and the radiator, showing the Hash trap and report mutller;

Fig. 19 is a transverse sectional View on a plane 15k-1t) Fig. 18;

Fig. 2O is a transverse sectional view through the barrel. the radiator. and the radiator casing, at an intermediate position in the length of the barrel. as. for instance, on a plane QO-QO Fig. 18;

Fig. Q1 is a longitudinal sectional view showing the mounting of themagazine and the cartridge feed mechanism therein;

Fig. QQ is a transverse section on an enlarged scale on the plane QQ-QQ Fig. 1.

.\ll the drawings are made to uniform scale, except Figs. 1 and 21 and the perspective views. which latter are approximately to scale.

The gun as illustrated is fitted with an air cooled radiator. but in practice this radiator may be removed and a water jacket fitted directly on the barrel to completely enclose the barrel from a point near the muzzle to a point a little rearward o thc chamber enlargement, thereby including the forward end of the chamber. The water jacket would be fitted with gland ends through which the barrel would work whilst the water jacket would be held steady.

The main structural features will be best understood by referencel to Figs. 3. 6. i, and 8. fixed in the forward end of a breech carriage in which an axially moving bolt is accommodated. and said bolt is engaged The breech end of the barrel is through a master pin bya bayonet slot key or "latch" Vto lock itin the breech carriage, the whole structure being adapted to recoil as one member; thereby compressing a re- 'storing spring which functions to cant the latch to locked position Whilst assisting to etl'ect reversal of the recoil movement; the boltl is closed by an independent resetting spring which is tensioned during the recoil act-ion.

The breech carriage 30, which is best seen in Fig. 6,'consists of two lateral 'cheeks slotted on one side as shown lat 231-32 for purposes Vhereinafter explained, offset at 33 its rear ends to carry a wrist pin' on which the latch 36 (Fig. 7) is mounted. The wrist pin 35 passes through the latch eyes 3T. and'is fixed in position by a wedge key 3H driven down behind a flat 239 on the middle length ot' the pin, said wedge key 3S .serving also to hold a spring 4() which is provided to butter the bolt at the back end otl its opening movement. 41 (Fig. 8l is the bolt.. lt is a slide litA between the forward cheeks of the carriage 3l); a lug i2 on the right side of its forward end works as a slipper in the slot til which forms a guide for it. A hole 43 in the rear end of tho bolt t1 accommodates a withdrawable master pin l--l which is held fixed by a bayonet catch '15 (see Fig. il.) lVhen this master pin is removed.l the gun cannot be operated as it forms the abutment of the bolt: it also serves for manually retiring the carriage and parts associated with it to set the gun for the first shot. After tiring the tirst shot the action is automatic so long as a charged magazine is in position. and so long as the trigger is held pressed. The master pin tt is a free running tit in the carriage guide slot 3Q. It is also a free running lit for the L-shaped notched slots 46-47 in the wing portions of the latch 36. The notches 4T of the slots 4G form abutment seatings for the master pin 44, so that when the latch 3G is set downward. as in Fig. 2. the bolt. il ispositively locked in the carriage Ill). with its forward end closing the breech of the barrel chamber 4S. cupped lug 49 on the top side of the rear end of the, latch 3G forms` an abutment for a ball-headed plunger 5t), against which acts ythe helical restoring spring 51. The rear end of this spring is housed in a tension adjusting screw cap rl`he lug 5S on the top side rear end of the bolt -ll mounted to carry the trace head 54 of the bolt resetting spring this is a helical spring in tension` having its for- 'ard end carried on a hook bolt 5G. the tension being adjustable by turning a knurled nut 57 which runs on the stem of the hook 5G. are ramp faces carried on a shoe 5f),

the fore-and-aft position of which is adjustable by means of a knnrled nut 61 accommodated in a gap in the butt head 60.

The striker faces 62 on the wings of the latch 36, contact with the shoe ramps 58 during the recoil movement of the breech carriage 30, and the position of the shoe 59 therefore determines the time in the recoil movement at which the latch releases the bolt; to allow it to move backward in the breech carriage'. 63 is an extractor spring hook, which, as usual, iS mounted on a pin 64 on the side of the boltl 41, with its hooked head 65 positioned to locate in a clearance space (3G in the breech of the chamber. to engage the base rim (57 on the cartridge case (5S. 69 is an ejector in the rear side ot the carriage 30; a slot 71 in the otl" side ot the bolt otl'ers clearance for the bolt movement past this ejector.

The whole ol` the mechanism between the butt and the radiator casing is contained in the body casing 72 (see Fig. 15); This casing is laterally slotted on the near side at T3 to permit ot` the ejccting ot the empty shell. at 74 to provide clearance for movement ot the master pin 41 with the bolt. and at T5 on both sides` to straddle the ends ot the latch wrist pin The hand grip and trigger assembly (Fig. 11) is an independent unit, and is set up in the lower part of the body casing T2 in the manner which will be best understood on reference to Fig. 2. The structural teatures ot' this assembly will be described later. Its mount-ing means consist in a hooked claw TT, engageable over a bridge pin T8 in the body casing T2. the rebated side edges T9 fitting into a rebate in the bottom ot the casing T2 (see Fig. 12). the assembly being locked in position by the engagement ot the overhanging nibs Ht) under the heel piece H1 of the butt head t3() (Fig. 1(1). The rear part ol' the bottom ol' the casing T2 is slotted as shown at Si? (Fig. 15). and is longitudinally grooved as shown at Sil at either side to engage .spigot ribsl 84 on the sides ot the butt head (if) (Fig. 13.)

lvpon the barrel Q9 a sleeve R5 (preferably constructed of aluminium) is slipped on. this sleeve carrying helically disposed thin radiator tins 86 between which and the casing 91 a little clearance is left. The radiator assembly is locked on the barrel between the abutment formed by the forward end 54T of the carriage 3L) and the clamping nutI 88 which is screwed on to the barrel muzzle (Fig. 19.) The nut H9 is formed with two or more wings S9 which set in slide guides 99 fixed iu the radiator casing 91. rl`he forward end ol the barrel is maintained in axial alignment with the casing 91 by these wing pieces. Riarwardly the barrel and breech parts are supported on wing pieces 92 which run in slide guides 921 formed in the forward part vol' the bod casing TQ.

The butt end ot the radiator casing 91 is made slightly conical to lit tightly on the slightly tapered forward end 95 of the body easing TQ. and is clamped thereon by a screw tightened band 91 so that said radiator casing 91 and said body casing T2 together form a complete enclosure for the gun parts, in which enclosure the barrelgthe radiator mounted on the barrel. the breech carriage, and the parts contained in the breech carriage are movable axially. Forward of the slide guides 90 in the raliator casing 91 the flash trap and report muftler device is contained. The casing 91 extends beyond the gun muzzle a few inches. and the mit H8 lorms a bell mouth 129 t'or the muzzle.A The forward end ot' the casing 91 is flanged inwardly as shown at 13H, leaving a central mouth 1211 ot' considerably greater diameter than the barrel bore. Intermediate the muzzle-bell l129 and the casing mouth 131. an open end cone'llz? is mounted. with its rear narrow end slightly t'orward ot the bell 129. This cone is centred and carried at its rear end by means of a spider lrame 151.'.fwh'ich is a push lit in' the casing 91: around its forward end it is tixed in the -casiug 91 Ab v rivets 131 or otherwise. so as to leave an annularspace between it and the casing. 'l`h'e wide end of the cone is incurled slightly to torni a ciicular lip 135. clearance space 13T is allowed between the rear end ot the cone 132 and the mouth otl the bell 129: this clearance space is shorter than a bullet length in order Ythat a bullet in passinginlo the conc 1:12,

will substantially block itsr 'narrow mouth and cause the following gases to divert into the annular space surrounding the conc. where they expand. and in passing l'orward to find exit through the annular vlip space atl 135 induce a l'ollowing draft ot cold air through the apertures in the body casing and over the radiator. ln passing tlirougll the annular space the flash is extinguished.

0n reference to Fig. 22 it will be noted that the inward tlutings 13R in the forward extensionrol' the body easing vT2 are located in alignment with the outward llutingsllf) in the butt end otl the radiator casing'91, the passages formed byA these flutes being open at the rear end (see 149. Fig. 1). These. passages 141 admit a current ol' air torwardly into the radiator space in the casing 91. air drat't being established'in the manner `hereinafter described.

lu the assembling ol' the guufparts. the bolt 41 and the latch ltl are set up in the breech carriage ill-i. sai'l carriageA being attached at its l'orward cnil to the screwed butt ol the barrel. the radiator being Iixed on the y barrel.

This assembly is inserted from the rear into its slide mountings in the body casing and radiator casing. which have been lirst clamped together by the band 94 and the master pin is inserted through the slots 74-32-46 and through the hole 43 in the bolt. Then the spring is connected to the hook 56'and the lug 53. The trigger assembly (Fig. 14) is then introduced by tak-v 80 under the heel piece 81 of the butt head 60. This locking in of the trigger assembly is ,best seen in Fig. 10. The operative parts of the gun can be removed Very rapidly by dismounting'the magazine, releasing theI housing latch 96 after backing olf the milled head screw 97, drawing the butthead backward, dropping down the trigger assembly, withdrawing the master pin, releasing the trace head 54 from the bolt lug 53, and drawing the barrel and breach carriage assembly out of the casings.

The trigger assembly comprises a hollow hand grip 98 in a slot in the rear part of which is mounted a safety latch 99 against which a spring 100 bearsto bring it normally to the outer position shown in Fig. 9. lVhen in this position the offset pin 101 on its top end working in the sl'ot 102 in the notch bolt 103 moves said bolt forwardly so thatv its head 104 enters the T path of the stop tooth 105 on the rear of i g ard 108.

ger 10G. The trigger is mounted on "7 carried above the top of the trig- The knuckle 109 on the shoulder of the trigger co-acts with the sear tappet 110. This tappet is mounted at its rear end on a pivot pin 111 and is normally pressed downward towards the trigger knuckle by a spring 112. )Vlien the trigger is in the safety position, the tappet 110 is held in low position by the spring 112 and in that low position it cannot engage the striker tail 113 of the sear 114. A spring 115 functions to hold the sear 114 downward against a stop pin 116. The sear tooth is engageable with a notch 117 in the tumbler 118. The tumbler is provide-.l with a toothed sector edge 119` and on the opposite side of its mounting pin 120 with a tappet tail 121. The Vtumbler and the sear and the scar spring are mounted in a slotted cavityv in the back end of the bolt with their tails protruding downward through the bottom of said slot, 122 is a cooking pawl capable of a little rocking movement limited by the shape of its seating in the nose portion of the trigger assembly frame. The cooking pawl is in alignment with the tappet tail 121 of the tumbler 118, The sector edge 119 of the tumbler meshes with a toothed rack 123 on the rear end of the striker 124. The striker is as usual terminated at its forward end in a hardened conical point 125 arranged to contact with the cartridge primer. Rearward of the conical point 125 a collar 126 fixed on it forms an abutment for the striker spring 127. The striker assembly is mounted in a tubular pocket 128 in the bolt. In the operative position of the trigger shown inV Fig. 10, the sear tappet 110 is lifted by contact therewith of the trigger knuckle 109, so that said tappet being thus raised against the pressure of the spring 112 is brought into the horizontal pat-h traversed by the Sear 114 during the recoil action of the gun parts. The trigger 106 cannot, however, be pulled except when the hand stock 98 is embraced so that the safety latch 99 is forced inward by pressure of the palm of the hand.

The access hatch 142 in the top side of the body casing 72 is closed by a slip-in cover plate 143, which at its forward end is 'formed with a nib 144 which takes under alip 145 in the forward part of the casing. Along its sides the cover p late 143 sets into a rebate 146,

`and it is locked 1n position by a hit-and-miss latch 147, which is eng'ageable below the rebate edges 146. 148 is a knurled nut, which carries the latch 147.

T he magazine 149 is a segmental box identical in transverse section (see Fig. 22) with standard service type magazine for shoulder arms. It is inserted at its delivery end 150 up into the feed throat 153 in the breech carriage. Its upper position is determined by its fitting into the pocket in said throat as in the caseof an ordinary service rifle, and

it is latched in position by a spring latch 151, which engages a hook staple 152 behind the throat 153. The weight of the magazine 149 and its contents is sustained by carrier arms 154-155, which are supported on a stud hanger 156, said stud hanger being adapted to slide on a fixed carrier pin 157. This pin projects forwardly from a collar 160, which is fixed on the butt collar 161 of the radiator, which is a tight fit on the Knox form exterior of the barrel chamber 48, that is, on the enlarged rear end of the barrel.

In this magazine, taper-shaped cartridges are packed so thatthey set in staggered order (the magazine width being greater than the diameter of one cartridge, but less than twice a cartridge diameter), the cartridge at the mouth of the magazine being lightly held by the inturned lips 167 on the cheeks of the magazine (see Fig. 5), but so that when the bolt 41 is moved forwardly, its' fore end takes behind the base rim of the cartridge and slides it endwise out of the magazine into the barrel chamber; as each .hanger 156 carries the cartridge in turn is thus slid out of the ma azine, the next cartridge in order is held 1n position in the magazine mouth for delivery into the barrel chamber in the next forward movement of the bolt.

The pivot pin 162 su ported bythe st-ud feed arm 158, which extends through a slot 165 and acting through the back spring 159 in the magazine supports and moves the platform 163 therein. The armA 158 is swung forwardly by a coiled wire spring 164 and functions through the platform to urge the cartridges in the magazine forward towards its mouth, whence they are taken one by one by the bolt action and delivered into the barrel chamber. This system of construction of the lmagazine and its mounting offers a positive advantage for reloading rapidly in action without disturbing the lay of the gun, as the gunner, while Vstill retaining the gun in position, may in a onehand movement, release the latch 151, swing the magazine on the pin 162, and slide it forward, thus bringing the hanger'156 off the pin 157. An empty magazineV is thus detached by an instant dexterous movement, and by a reverse lmovement .a full magazine inserted. Continuity of firing is therefore interrupted only for a period of a second or two when a magazine is exhausted, and as each magazine contains a very large number of cartridges, the gun is thus qualified in a special degree for repeated Iprolonged bursts of firing, which very frequently is a consideration of major importance.

The operation of the gun as an automatic gun is as follows A magazine being placed in position, and a cartridge inserted into the chamber by once manually operating the locking mechanism by reciprocating the vbreech carriage byv means of the master pin 44, the trigger 106 is pulled, whilst at the same time the safety latch 99 is inclosed by pressure of the palm of the gunners hand, thus'zwithdrawing the check 103 and allowing the trigger to be moved. vIn the pulled position, the trigger bears the sear tappet 110 upward from theridle position shown in Fig. 9 to t-he firing position shown-in Figs. 10 and 11. The upward movement of the tappet 110 acting against the tail 113 of the sear114, draws the tooth of the sear out of engagement with the notch 117 of the tumbler 118. The striker spring 127 being thus liberated, drives the striker 124 forward, causing its firing point 125 to strike the cartridge rimer and explode the cartridge. The bulet passes out of the barrel 29 through the bell mouth 129 and thence through the cone 132. As it passes from the barrel muzzle into the narrow mouth of the cone 132 the fiery gases following it are diverted laterally and are splayed outwardly, and pass through thel apertures in the spider 133.-

The high pressure gasesthus diverted into -the annular space surrounding the cone 132,

disposed radiator fins, abstracts heat from them. The flash'is extinguished before it reaches the tube mouth 131. perature of the barrel is practically uniform on all sides of it, bending and twisting of the barrel under prolongedfire does not take place, andthe accuracy of the gunners aim is therefore not substantially disturbed. The reciprocating movement of the barrel and the radiator tins operates to procure effective washing cont-act of the cooling air with the metal surfaces, thereby exalting the rate of transference of heatthrough the radiator tothe air. In addition to the cooling air indrawn through the fiuted passages 141, air is also drawn through the body casing and through the clearance space in the bottom part of it where the magazine support 157 Vis located.` There is thus a. considerable transverse section .through which air may enter the radiator, so that va quite free flow of air is available for movement through the radiator. TheV cone 132 sound muffler, so that the noise of the explosions of the gun is deadened, and it is`difticult at a little distance tolocate the p'osition of the gun by the sound of the fire.

When the cartridge charge is exploded, recoil takes place andtheV barrel 29 and breech carriage30 and the assembly of parts supported therein, move bodily rearward (see Fig. 4). In the recoil movement from the position shown in Figs. 2, 3, and 9 to the position shown in Fig. 4, the restoring spring 51 isV compressed. When the strikers 62 on the latch 36 contact with the shoe ramps 58, the latch is lifted so that its long slot Vis brought up to alignment with the master pin'44 which is carried in the bolt. Immediately the latchfis so cleared, the back pressure of the gases in the barrel 29 acting through the empty shell opera-tes to recoil the bolt 41,l and simultaneously with thisrecoiling movement of the bolt. the reaction on the barrel assembly assisted to a greater or less extent 'by the restoring spring 51, according to its tension adjustment, effects the bodily return of the barrel and breech carriage assembly forward. `The backward movement of the bolt continues `according vto the adjustment ofthe bolt resettingspring 55,'the buffer spring 40 taking valso functions to a limited extent as a v the impact ofthe bolt before the master pin strikes the back end of the latch slot 46. At this point the bolt has moved back its full vtravel (Fig. 5), dragging the empty shell of the cartridge 68 back with it by means of the extractor hook 63. In this movement the spring hook 63 moves' the cartridge attaining the across the nose of the bolt, bringing the far edge of its lange into alignment with the ejector 69, and clearing the back end of the barrel chamber, the empty shell is ejected tothe right, out through the clearance space 31 in the side ofthe breech carriage, and out through the opening 7 3 in the right side of the body casing 72. vForward return movement of the bolt now taking place rapidly, the barrel and breech carriage assembly having meantime moved forward to the normal advanced position, a new cartridge which has come up into the magazine mouth as soon as the top of that mouth was cleared when the underside of the bolt passed back over it, comes into the path of the bolt, and the bolt, in advancing, drives said cartridge into the barrel chamber.

The entry of the straight portion into the notch portion of the latch slot. 46 is curved for the purpose of. imposing a downward pressure on the latch whenv the master pin contacts `with it, to ensure that .the latch will close rapidly as soon as the master pin 44 lreaches the notch position and thus to ensure that abutment will be established for the bolt instantly upon its firing position. This is very important, as the sear is tripped just as the closed position of the bolt is atta-ined, and the abutment for the bolt must be established by fully closing down the latch 36 on the master pin before the reaction of the explosion is taken by the bolt.

The cooking of the trigger mechanism is eiected automatically. In the recoil movement (about to begin as shown in Fig. 10), the tail 121 of the tumbler 118 strikes the cooking pawl 122, andthe tumbler is thus reversed from the position shown yin Fig. 10, to the position shown in Fig. 11. Meantime, the tail of the soar 114 has passed back clear of the sear tappet 110, and the scar is restored by its spring 115, so that its tooth engages the notch 117 of the tumbler, thus holding the tumbler in cocked p0- sition. In this reversing` movement of the tumbler, its toothed edge 119, meshing with the rack 123` retires the firing pin 124, thus compressing the firing spring 127. In the next forward movement of the carriage, a new cartridge having been introduced into the chamber of the barrel as already described, firing takes place automatically. The gun will continue to operate automatically in this manner so long as the trigger is held pulled and cartridges are available in the magazine. It may be operated as a singlerer by pulling the trigger-and releasing it rapidly before the bolt is restored to firing position after the recoil. The adjustments necessary to. time the gun and to ensure eiective movement of the several elements in their proper relation are readily made upon contacting with which ,said bolt house through accessible devices. Practioall only three adjustments are necessary: First y, the tensioning of the bolt-resetting spring 55 by means of the milled nut 57; secondly, the tensioning of the restoring spring 51 by means of the milled capn 52; and thirdly,

the positioningv of the shoe 59 by means ofthe milled nut 61. The rate of fire may be varied whilst the gun is in automatic operation by adjusting the nut 61, thereby to move the shoe 59 There is necessarily a limited range of movement for the shoe 59. In its extreme permissible forward position, maximum rapidity of fire is obtained, whilst in its extreme rearward position the gun is adjusted for automatic fire at the slowest rate for which it is structurally adapted.

What I claim as my invention and desire to secure by Letters Patent is 1. A machine gun having a recoilable barrel, a carriage attached to said barrel as a rearward extension thereof and axially slidable therewith, a body casing surrounding said-carriage, an axially sliding bolt, a withdrawable master pin mounted in the rear end of saidv bolt and serving as an abutment therefor, a drop down latch for said bolt housed in said carriage said latch being automatically opened in the recoil movement ot the carriage and automatically closed in the vforward return movement thereof, trigger mechanism mounted in the body casing, means for automatically cooking and firing the gun engageable by said trigger mechanism, and means for varying the rate of fire during action.V y

2. A machine gun having a recoilable barrel, a carriage attached to said barrel as a rearward extension thereof and axially slidable therewith, a body casing surrounding said carriage, an axially sliding bolt, a. withdrawable master pin mounted in the rear end of said bolt and serving as an abutment therefor, a drop down latch pivotally carried at Aits rear end in the rear end of said carriage, L-shaped slots in the sides of said latch adapted to receive said master pin, automatic means for lifting said latch to permit free backward movement of said bolt during the recoil motion of the carriage, and means for restoring said latch to looking position during the forward movement of t-he carriage consist-ing of a cupped lug on the top side of the rear end of said latch and ajball-headed spring plunger abutting in said lug. i

3. A machine gun having a recoilable barrel, a carriage attached to said barrelv as a rearward extension thereof and axially slidable therewith, a body casing surroulfding said carriage, an axially sliding bolt, a withdrawable master pin mounted in the rear end of said bolt, a (pivoted dropdown latch for in said carriage, slots in the forwardly or backwardly.

rearward extension thereof and axially slidable therewith, a body casing surrounding sald carriage, an axially sliding bolt a wlthdrawable master pin mounted in the rear end ofl said bolt, a pivoted drop down latchV for said bolt housed in said carriage, slots in the sides of said latch adapted to receive said master pin, a cam surface on the forward end 0f each of said'slots, strikers on the base of said latch, an adjustable ramped shoe inv said body casing adapted to be engaged by said strikers, and means for manually positioning said shoe.

5. In a machine gun in which the bolt slides axially in a breech carriage which is fixed to the barrel and recoils with it, a spring operated firing pin housed in the bolt, a tumbler pivotallymounted in the bolt, a rack on -the rear end of said pin meshing with a secto'r on said tumbler, a tappet tail on the tumbler engageable with a cooking pawl in the trigger assembly, a tailed sear mounted in the bolt and engageable with the, tumbler and a tappet movable by the trigger to trip said sear and thus release the tumbler and tiring pin.

6. A machine gun having a recoilable barrel, a carriage attached to said ba'rrel as a rearward extension thereof and axially slidable therewith, a body casing surrounding said carriage, anl axially sliding bolt, a withdrawable master pin mounted in the rear end of said bolt, a pivoted drop down latch for said bolt housed in said carriage, slots in the sides of said latch adapted to receive said master pin, a cam surface on the forward end 0f each of said slotsga cupped lug on the top side of the rear end dfosaid latch, a ball-headed spring plunger abutting in said lug, a lug on the rear top side of said bolt, a bolt resetting spring adapted to`\en gage said lug, and means for adjusting thek tension of said resetting spring and of said spring plunger.

7 A machine gun having a recoilable barrel, a carriage attached t0 said barrel as a rearward extension thereof and axially slidable therewith, a body casing surrounding said carriage, an axiallyv sliding bolt, a withdrawable master pin mounted' in the rear end of said bolt, a pivoted drop down latch`l for said bolt housed in said carriage, slots in the sides of said latch adapted to receive said master pin, a cam surface on the forward end of each of said slots, a bridge pin mounted in said body casing, a trigger frame, a hook on said frame engageable with said bridge pin, projecting nibs and rebated side edges on the t'rlgger frame, a rebate in the bottom of said bodyl casing to engage said rebated side edges, a butt head, and a heel piece on said butt head adapted to be engaged by said projecting nibs.

8. A machine gun having a recoilable barrel, a carriagel attached to said barrel as a rearward extension thereof and axially slidable therewith, a body casing surrounding said carriage, an axially sliding bolt, a withdrawable master pin mounted in the rear end -of said bolt, a pivoted drop down latch for said bolt housed in said carriage, slots in the sides of said latch adapted to receive said master pin, a cam surface on the forward end of each of said slots, a cupped lug on the top side of the rear end of said latch, a ball-headed spring vplunger abutting in said lug, a lug on the rear top side of said bolt, a bolt resetting spring adapted to engage said lug, means for adjusting the tension of said resetting spring and of said spring plunger, a releasable housing latch, and a releasable spring trace head.

9. A machine gun having a recoilable barrel, a carriage attached to said barrel as a rearward extension thereof and axially slidable therewith, a body casing surrounding said carriage, an axially sliding bolt, a withdrawable master pin mounted in the rear end 0f said bolt, a pivoted drop down latch for said bolt housed in said carriage, slots in the sides of said latch adapted to receive said master pin, a. cam surface on the forward end of each of said slots, spring means adapted to return the barrel and carriage, and independent spring means adapted to independently return said bolt.

10. In an automatic machine gun having a breech carriage attached to the rear end of the barrel, and an axially sliding bolt and a drop latch therefor housed in the breech `carriage, a withdrawable master pin detachably-.,carried in the bolt and forming engaging means between the bolt and the latch, said master pin being extended to protrude laterally through slide slots in the breech carriage and thebody casing.

In testimony whereof I aiix my signature.

JOHN (IR. MCCRUDDEN. 

